1. Field of the Invention
An enclosure is cooled by a compact, efficient refrigeration system incorporating an air-to-air heat exchange economizer.
2. Description of Related Art
There are numerous manufacturers of mechanical, refrigeration based air conditioners and numerous manufacturers of air-to-air heat exchangers. Both types of equipment are applied for the cooling of shelters, cabinets or enclosures, which often contain electronic equipment, or other heat generating devices that do not require, nor desire, ventilation air. The introduction of ventilation air, or outside air, directly into the enclosure is actually undesirable because of contaminants. Each method of cooling has limitations. Both type devices use closed loop systems, by which the recirculating air inside the enclosure never comes in contact with outside air during cooling, thus eliminating the potential for contamination of the electronics, or other sensitive materials, inside the heat generating equipment enclosure. An air-to-air heat exchanger is a device that transfers energy from one air-stream to another, without actual mixing of or contact between the two airstreams. Air-to-air heat exchangers can be a plate type, rotary type or heat pipe type. For systems requiring closed loop cooling, the rotary type heat exchanger is not used because of the difficulty in insuring that there is no leakage between air streams. For purposes of the present invention, only air-to-air heat exchangers, that are xe2x80x9csensiblexe2x80x9d heat transfer devices, are considered, because they transfer heat without transferring moisture or contaminants.
It is common for the heat load inside an enclosure to be high enough to require some cooling for the majority of the year. Depending on the desired internal enclosure temperature, a particular cooling system will be selected. For internal temperatures lower than the warmest ambient temperatures, a mechanical air conditioner is used. If internal temperatures are allowed to be higher than ambient, it is possible to use an air-to-air heat exchanger. It is also common practice to install a mechanical air conditioner in parallel with an air-to-air heat exchanger. In this way, the air-to-air exchanger can operate when the ambient temperatures are sufficiently lower than the desired internal temperature to achieve the desired cooling. When the ambient temperature is too warm for the heat exchanger to achieve all required cooling, or when the ambient temperature is higher than the desired internal temperature, a mechanical air conditioner will operate.
The use of outside ambient air as a heating/cooling means is common. The provision of alternate flow paths through air conditioning units for cooling, ventilation, exhaust and tempered ventilations is old with Terry et al, U.S. Pat. No. Re 22,584, issued Dec. 26, 1944, an example.
It is old in the art to combine a refrigeration unit and an air heat exchanger to improve efficiency. With occupied dwellings, ambient air is introduced into the dwelling as fresh air and stale dwelling air is exhausted. The patent to Bishop et al, U.S. Pat. No. 5,447,037, issued Sep. 5, 1995, is an example of such use with the controls that can be incorporated.
The patent to R. Travers, U.S. Pat. No. 5,239,834, issued Aug. 31, 1993, is an example of a refrigeration unit used in parallel with an air-to-air heat exchanger for temperature control of an enclosure. Both the exchange of ambient air with enclosure air and prevention of air exchange are disclosed. The primary concern is for temperature control of perishable and/or consumable food products. It is desirable to prevent contaminated ambient air from entering the enclosure. Contamination of the enclosure air is prevented by use of an air-to-air heat exchanger in parallel with a refrigeration/air conditioning unit.
The present invention combines and integrates a mechanical air conditioning system and an air-to-air heat exchanger or economizer. The unique combination of the two systems allows for three modes of operation depending on the difference between ambient air temperature and desired enclosure internal air temperatures with a fourth mode available for extremely cold ambient temperature. A system of dampers and controls determine which operating mode is employed.
Enclosure air takes the same path through the cooling unit, heat exchanger and refrigerant unit and heater, regardless of ambient air temperature. During periods when ambient air temperatures are low, cooling of enclosure air is by air-to-air heat exchange with the refrigeration unit idle. Enclosure air flows through the air-to-air heat exchanger with heat transfer taking place as ambient air is passed through the heat exchanger. Sensible energy is transferred from the warmer air stream to the cooler air stream, whereby the warm entering enclosure air stream is cooled, and the cooler ambient air stream is heated. When applied to enclosures housing electronic equipment, the warmer enclosure interior air path is cooled based on the outside temperature. It is impossible to cool the interior air stream below the ambient temperature with only an air-to-air heat exchanger, unless special indirect cooling methods are used which involve complicated systems.
When ambient air temperatures are cooler than desired maximum enclosure temperatures, but warmer than desired enclosure minimum temperatures, refrigeration is employed concurrently with the air-to-air heat exchange. The ambient air is used to absorb heat, first from the enclosure air stream, followed by a second absorption of heat from the refrigeration condenser.
When ambient air temperatures are higher than enclosure maximum air temperature, cooling is by the refrigeration unit alone. No ambient outside air is passed through the air-to-air heat exchanger but is passed only through the condenser of the refrigeration unit to indirectly remove heat from the enclosure air stream.
Extremely low ambient air temperatures may require heating of the enclosure air.